<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .main p:nth-child(1){
            border:1px solid red;
        }
        .main p:nth-of-type(1){
            border:1px solid red;
        }
       /*.main p:first-child{*/
       /*     border:1px solid red;*/
       /* }*/
        .a1, .a2, .a3{
            width: 100px;
            height:100px;
            border:10px solid red;
            padding: 20px;
            margin:20px;
        }
        .a1{
            box-sizing: border-box;
        }
        .a2{
            box-sizing: content-box;
        }
        .a3{
            box-sizing: inherit;
        }
        .main{
            border:1px solid blue;
        }
        .main::after{
            content: '';
            display: block;
            height:0;
            visibility: hidden;
            clear: both;
        }
        .main-son{
            width: 200px;
            height:100px;
            border:1px solid blue;
            float: left;
        }
    </style>
</head>
<body>
    <div class="main">
        <div>00</div>
        <p>1</p>
        <p>2</p>
        <p>3</p>
        <p>4</p>
    </div>
    <div class="a1">www</div>
    <div class="a2">wwww</div>
    <div class="a3">wwwww</div>
    <div class="main">
        <div class="main-son">dasdad</div>
    </div>
    <script>
        function test(){
            console.log(arguments)
        }
        test(12,8,7)
    </script>
</body>
</html>
